Onkyo TX-DS575

[frankusb]

The receiver is going into protect mode when switching inputs or enabling/disabling A or B speakers on the front panel. I removed the protect signal from the main microprocessor and the system played normally on FR and FL speakers from an analog input. I measured the protect signal and it's attached.



I checked the idle current adjustment on each of the 5 channels and adjusted them slightly (less than 2mV). I checked the DC offset of each channel and it was very small.

I'm guessing to diagnose further I'll need to figure out which one or more of the channels is triggering protect. What doesn't make sense to me is why changing inputs would cause protect to trigger.

Any other thoughts on what I might look at?

[frankusb]

Thank you redwire for your help. I got the part in the mail today and replaced it and everything is working perfectly. Now I have 9 extra RN1241s. Q3383 has been replaced and no more protect shut offs or popping from Speaker B.

[petehall347]

there is overcurrent protect .i suspect its that . try without speaker loads first

[redwire]

The fact that protection trip happens when switching speakers on/off is not good. Normally a power amp doesn't care about this happening- unless it's got problems or a DC offset present on a channel but you say there is none. Are you for sure measuring upstream of the output relays?

If a pwr amp failure (i.e. output transistor shorted) ever had happened, it can damage electrolytic capacitors and sometimes these get forgotten when replacing semi's.
Prot DC detect filter cap like C581 on V-PRO. It will false-trigger protection on thumps or low bass if it goes low value. Or the feedback caps get damaged like C505, C506, C607, C608, C1503- if these short then you get a DC offset or the amp cannot go to 0V quite right.

I would ID the bad channel by checking DC offset on each channel, comparing spkrs on/off with a load resistor present.
The pre-amp could be making huge thumps if there's a problem there, such as the muting (bad muting transistor) is not working.

[frankusb]

there is overcurrent protect .i suspect its that . try without speaker loads first

The only time I had speakers hooked up was to test 2 channels. The rest of the time no speakers are connected.

[frankusb]

The fact that protection trip happens when switching speakers on/off is not good. Normally a power amp doesn't care about this happening- unless it's got problems or a DC offset present on a channel but you say there is none. Are you for sure measuring upstream of the output relays?

If a pwr amp failure (i.e. output transistor shorted) ever had happened, it can damage electrolytic capacitors and sometimes these get forgotten when replacing semi's.
Prot DC detect filter cap like C581 on V-PRO. It will false-trigger protection on thumps or low bass if it goes low value. Or the feedback caps get damaged like C505, C506, C607, C608, C1503- if these short then you get a DC offset or the amp cannot go to 0V quite right.

I would ID the bad channel by checking DC offset on each channel, comparing spkrs on/off with a load resistor present.
The pre-amp could be making huge thumps if there's a problem there, such as the muting (bad muting transistor) is not working.

I measured output voltage between positive and negative after the relays but I probably only got 2 channels of good measurements in stereo mode. Thanks for that hint.

I don’t know the history as it’s from the trash heap.

What type of load resistor should I use?

The pre-amp muting would fit the protect triggering when changing inputs. And I did notice unexpected popping when enabling B speakers during audio testing. I can’t recall if I tried switching inputs but that seems like a good test.

[frankusb]

I thought I attached the schematic for this but I don't see it.

[redwire]

Need to narrow down where the problem is. Is the popping occuring in all channels? Might have to disable the protection DC detect.
Wild guess, there is a problem with the muting circuit or the audio switching circuit.
Or it could be a power amp channel but you can measure the DC offset (must be upstream of prot relay) and see if a channel is sick. Headphones are after the relay so not useful I think.
The "multi-channel" outputs/inputs could be checked if they are OK. I don't have time right now to give a detailed strategy.
Try have fun and play around with it, look for anything.

[frankusb]

Need to narrow down where the problem is. Is the popping occuring in all channels? Might have to disable the protection DC detect.
Wild guess, there is a problem with the muting circuit or the audio switching circuit.
Or it could be a power amp channel but you can measure the DC offset (must be upstream of prot relay) and see if a channel is sick. Headphones are after the relay so not useful I think.
The "multi-channel" outputs/inputs could be checked if they are OK. I don't have time right now to give a detailed strategy.
Try have fun and play around with it, look for anything.

No need to take any more time, I have items to research (for fun - it really is just fun, I have no use for this receiver but it's a shame to see it thrown away). Thank you for your time thus far.

Protect is currently disabled altogether, all types. So I believe I can measure after the protection relays (RLC are hard to get to before the relay with the heat sink) if I enable 5 channel stereo mode.

I too agree with muting or audio switching. I believe after some more data collection, that is where I will focus, trying to remove those from the protect circuit and see what protects I can leave enabled.

[frankusb]

In 5 channel stereo mode, CD input, warmed up:
FL: -10mV
FR: -2mV
C: -1mV
SL: 0mV
SR: -10mV

[frankusb]

I-Pro has 5 transistors, Q527, Q528, Q627, Q628 and Q1514. V-Pro has 5 resistors, R1528, R658, R657, R553 and R554. The V-Pro resistors feed into Q582/Q581. The output of Q582/Q581 then feeds along with the output of the I-Pro transistor into Q583 which is the Protect signal.

I assume I-Pro is current protect and V-Pro is DC detect?

[frankusb]

Switching inputs does not make any noticeable sound on the FR and FL speakers. All inputs tested. Only the FR and FL speakers are connected for all tests (A speakers).

The only popping on the FR and FL speakers is heard when the A speakers are enabled and the B speakers are turned on or off. The pop when turning on the B speakers is not a lot. The pop when turning off the B speakers sounds like something you would want to avoid.

If I turn the A speakers off and on, the speakers do not pop. If I turn the A speakers off, then turn the B speaker on and then off, then turn the A speakers on, they will pop. Followed by a pop when turning off the A speakers. Subsequent on/off cycles do not pop unless I involve the B speakers.

[redwire]

I-Pro has 5 transistors, Q527, Q528, Q627, Q628 and Q1514. V-Pro has 5 resistors, R1528, R658, R657, R553 and R554. The V-Pro resistors feed into Q582/Q581. The output of Q582/Q581 then feeds along with the output of the I-Pro transistor into Q583 which is the Protect signal.

I assume I-Pro is current protect and V-Pro is DC detect?

V-PRO should be called V-PROTECT, it's a summation of the outputs of all channels with low pass filter C581. It needs around 1VDC seen to trip.
I-PRO should be called /I-PROTECT, it goes low if any power amp sees over-current OR V-PRO is asserted. They get tied together.

It can be perfectly normal for the amp to thump and activate the protection circuit, if there are big thumps coming into the amplifiers.

Your idle DC offsets look reasonable. It needs to be several volts for many 100's milliseconds before the DC detect gets activated.

[frankusb]

I've got some data that I don't understand. I disconnected JL501B (+24V, I-PRO, V-PRO, REM_EN, GND and SUR_EN) from the surround/remote amp board hoping to isolate the source of the protect between the two amplifier boards, and it half worked. The protect is no longer being triggered by switching between inputs (DVD, VIDEO 1, 2, etc). But it still is being triggered by toggling Speaker B on and off (mostly off).

What could be causing the A speakers to pop (and trigger protect) just by toggling the B speakers?

[frankusb]

I'm guessing FMUT to NCVD-6566 is where I should be looking.

[redwire]

I think JL501 goes to just include the surround channels in the protection circuit. The front channels are always hardwired to PROTECT (which is the summation of all channels V-PRO and I-PRO) by Q583.
I can't find the Speaker A/B switch on the schematic.
If the MCU activates MUTE while switching the A/B relays? then it looks like the muting circuit is making thumps.
If it's just a plain speaker switch, then that looks a front power amp channel has DC offset.

[frankusb]

I think JL501 goes to just include the surround channels in the protection circuit. The front channels are always hardwired to PROTECT (which is the summation of all channels V-PRO and I-PRO) by Q583.

It also includes the relay controls.

I can't find the Speaker A/B switch on the schematic.

It's in the switch array in NADIS-6576. 3rd row, 3rd column.

If the MCU activates MUTE while switching the A/B relays? then it looks like the muting circuit is making thumps.

I think it does activate MUTE while switching B on or off. I am suspecting either MUTE or whatever switches between surround and remote speaker input signals. I will look at this tonight.

[frankusb]

I think I found a problem responsible for the B speaker popping. It's only on the left channel. What's happening is when enabling the B speakers, I believe the output of Q3383 is sitting at -2.0V. So the output of Q3181 gradually drifts down to -2.0V. Then when disabling the B speaker, it pops back up to around 0V.

I measured the output of Q3483 to compare and it's sitting at 0V.

This is on NCVD-6566. I disconnected P601 so it's not connected to anything.

[frankusb]

If anyone can suggest a replacement part for a Toshiba RN1241 I would appreciate it.

[frankusb]

Would you trust this?

[redwire]

I don't know, it looks like a reasonable store 98.5% feedback. You can swap the muting transistor with another from an unimportant section to confirm it is the problem.
The RN1241 has an internal 5.6kΩ base resistor so it would not test the usual E-B junction 0.7V